1. Technical Field
The present invention relates to a technique to discharge fluid from an ejection head having minute ejection nozzles by supplying a driving voltage waveform to the ejection head.
2. Related Art
So-called an ink-jet printer is capable of printing a high-quality image by discharging ink of an accurate amount to accurate positions from minute ejection nozzles, and is nowadays widely used. It is also considered to be possible to manufacture various minute components such as electrodes, sensors, or biochips by discharging various types of fluid instead of ink toward a substrate using this technique.
In the technique as described above, a specific ejection head is employed so as to enable discharge of fluid such as ink by an accurate amount at accurate positions. Although there are several methods as methods of driving the ejection head, a method of deforming minute fluid chambers provided in the interior of the ejection head by actuators, and causing the fluid in the fluid chambers to be discharged from the ejection nozzles by using the capacity change of the fluid chambers at that moment is known as a representative method. As the actuator, a piezoelectric element is widely used because it has a high responsiveness and is able to generate strong force.
In order to print an image quickly while maintaining the quality, it is necessary to discharge the ink at a high repetition frequency while maintaining the accuracy in the amount and the position of the ink to be discharged. Therefore, employing a driving voltage waveform to be applied to the actuator such as the piezoelectric element, which has a trapezoidal shape in which a rising portion and a lowering portion of the voltage are sloped, instead of a driving waveform having a simple rectangular waveform is contemplated (JP-A-7-178907).
However, when an attempt is made to apply the trapezoidal-shaped driving waveform in order to discharge the fluid of an accurate amount at the high repetition frequency, the following problems arise. In a step of generating the driving voltage waveform to be applied, there is a problem such that a large power loss occurs in order to generate a voltage waveform which changes in a sloped manner at the rising or the lowering portion of the waveform. When the actuator includes a capacity component as in the case of the piezoelectric element, there is also a problem such that a reactive power for charging and discharging electricity with respect to the capacity components of the actuator is consumed on the side of the driving voltage waveform generating circuit, and hence the power efficiency is further lowered. Furthermore, since the dissipated power is transformed into heat, it is required to release heat from the driving voltage waveform generating circuit, resulting in a larger circuit.